[Cerrado] Changing the default language on a staging site

Hi!
I've looked at some support threads, and I think I know the answer. But just to make sure: If I change the default site language from Norwegian (.no) to English... Will the .no be replaced in both content and design with what came from the pages under the .no/en/ translations and become the main language and design of the site, what you see when you arrive at accessoslo.no eventually? My client is thinking of only having english as language, and have quite lot of changes they want to make in the english version, and I wonder if I should change the default language before I make the changes.
All the best,
Guro